In the conventional three-dimensional printing technique, it is common to slice a three-dimensional object model constructed by software such as a computer aided design (CAD) program into a plurality of thin cross-sectional layers. Then, a printing head of a three-dimensional printing apparatus may move along a printing plane above a printing base and output materials according to coordinates of a space (e.g., a space formed by an X-axis, a Y-axis, and a Z-axis) constructed in the three-dimensional object model, so as to dispatch the forming material in a desired shape of the cross-sectional layer. The forming materials deposited may be cured naturally or by heating or light irradiation, so as to form the cross-sectional layer as desired. Hence, by moving a printing module along a forming axis (i.e., Z-axis) layer-by-layer, the cross-sectional layers are stacked sequentially along the forming axis (i.e., Z-axis), thereby forming the three-dimensional object by curing the forming material layer-by-layer.
However, the edge of a real object is linear and continuous, whereas the edge of the three-dimensional object produced by three-dimensional printing is not necessarily continuous, as the object is formed by stacking the thin cross-sectional layers. For example, in the case where the edge of the three-dimensional object model along the Z-axis is declined, if the three-dimensional object is sliced into a plurality of cross-sectional layers, there will be a difference between the edges of the vertically adjacent cross-sectional layers after the slicing, and the inclination is not being presented as linear and continuous. When the cross-sectional layers have a greater thickness, there may even be a pattern visible to naked eyes.
To eliminate or reduce the pattern, it is common to compensate edge portions of the cross-sectional layers by slope compensation or Gaussian smoothing. Slope compensation refers to compensation by linear interpolation based on a slope of a line connecting the edges of two adjacent cross-sectional layers. However, the slopes at the left and right ends of the same cross-sectional layer may not be necessarily consistent. Thus, it may be difficult to determine the extent to which the compensation is made. Gaussian smoothing, on the other hand, is performed by carrying out Gaussian smoothing operation on the edge portion of each cross-sectional layer to reduce the edge difference between each cross-sectional layer and the adjacent cross-sectional layer. However, Gaussian smoothing may result in a greater difference between the three-dimensional object eventually printed and the three-dimensional object model constructed by the software. How to suppress the pattern without resulting in distortion thus remains as an issue for the researchers in the field to work on.